This invention relates to the preparation of a novel glass based container. More especially, this invention relates to the preparation of a decorable container which is resistant to both scratching and shattering and which can be economically recovered and recycled for further use.
Glass containers are manufactured in a variety of colors. When such containers are recovered for recycle, it is typically necessary to separate the recovered containers on the basis of color.
In accordance with this invention, there is prepared a glass based container which has increased scratch and shatter resistance and improved decorability, and which can be readily recovered for recycling without separation by color.
More particularly, in accordance with the practice of this invention, there is prepared an annealed glass container having at least a portion of its external surface coated with a protective, decorable, water removable, organic polymeric film, said polymeric film being capable of removal by aqueous medium such that the glass base material can be recovered, recycled, and/or reused.
It is well-known that glass in its pristine condition is a very strong material, but that scratches and abrasion on the glass surface will considerably decrease its strength. Consequently, glass articles, for example, containers such as jars, bottles, tumblers, and the like, have maximum strength immediately after formation; however, this strength diminishes when the glass article surface contacts other surfaces as may occur during the inspection, handling, packaging, shipping and consumer use of the article.
To overcome this problem, there has been a great deal of research in the glass industry towards development of thin, tenaciously adhering, lubricious, damage-preventive coatings which preserve the glass strength and allow the glass article to be handled and used by the consumer.
In the glass container industry, such damage-preventive coatings have been primarily of two types. In one type, the container is coated with a thin organic coating at the "cold end" of the annealing lehr where the temperature is in the neighborhood of 200.degree.-400.degree. F. These coatings have been polyoxyethylene stearate as in U.S. Pat. No. 2,813,045 (Abbott); polyethylene as in U.S. Pat. No. 2,995,533 (Parmer and Schaefer), and U.S. Pat. No. 2,965,596 (Scharf); or other organic materials as in U.S. Pat. Nos. 3,445,275 (Bogart); 3,487,035 (Bogart); 3,357,853 (Pickard) and 3,296,174 (Pickard).
In the second type of coating, the glass container is first coated with metal oxides such as the oxides of tin, titanium, vanadium, or zirconium at the hot end of the annealing lehr where the temperature is in the range of 1000.degree. to 1100.degree. F. and then overcoated with a protective organic coating at the cold end of the lehr. Such dual coatings are illustrated in U.S. Pat. Nos. 3,323,889 (Carl and Steigelman); 3,425,859 (Steigelman); 3,598,632 (Long); 3,554,787 (Plymale); 3,498,825 (Wiens); 3,418,154 (Rawski); 3,420,693 (Scholes and Pickard); 3,445,269 (Bruss et al.); 3,407,085 (Kitaj, et al.); 3,414,429 (Bruss, et al.); and 3,352,707 (Pickard). The above types of coatings are "production line" coatings because their application is accompished as part of the forming and annealing sequence. The disclosures of these patents are incorporated herein by reference.
The application of a water-soluble scratch-resistent coating to a glass surface is described in Benford and Mielke, U.S. Pat. No. 3,577,256. A dilute aqueous solution containing at least three water-soluble ingredients -- an acrylic polymer, a polyoxyethylene glycol, and a melamine-formaldehyde resin -- is applied to the surface of freshly drawn glass tubing. This coating provides temporary resistance against scratching during handling, and is intended to be removed by thermal decomposition during subsequent annealing of the tubing. The coating can also be removed by washing with water. The coating is not a part of the final manufactured article, and hence, it cannot provide resistance to either scratching or shattering of that article. Since the function of the coating is to provide scratch protection but not resistance to shattering, very thin coatings are adequate and it is not essential that the coating materials be of sufficiently high molecular weight to be film forming.
Glass containers are sometimes fractured by dropping or other accidental misuse. This problem is particularly acute when the glass container has pressurized contents such as in the case of beer or carbonated soft drinks.
In accordance with this invention, there is provided a coating for glass containers which is capable of retaining broken glass fragments upon fracture of the glass container so as to reduce the incidence of accidental injury.
Attention has been directed to this problem, in the recent past. For instance, German patent disclosure No. 2,026,909, published Dec. 10, 1970, discloses coating a glass container with a loosely or firmly adhering plastic material designed to form a "bag" which retains glass fragments when the container is broken. The film is formed by fusing powdered polyethylene to the glass bottle. German patent document No. 2,149,219, published May 25, 1972, discloses coating glass containers with a film coating of a hydrolyzed ethylene-vinyl acetate copolymer. U.S. Pat. No. 3,178,049 discloses a light, composite glass container having a wall thickness of about 0.15 to 0.70 millimeters surrounded on the outside by an envelope of a thermoplastic material having a wall thickness at least equal to the glass. U.S. Pat. No. 3,415,673 discloses glass containers which are made resistant to breakage by coating the exterior surface with a thin, highly adhesive layer of plastic consisting essentially of a copolymer of ethylene. A primer is used to tenaciously adhere the copolymer to the surface of the glass article.
The present invention improves over these types of coatings and provides an economical and expedient method of coating glass containers to provide the capability of retaining glass fragments upon fracture. Furthermore, this invention provides a convenient and economical method of separating and recovering the glass and the coating material from used containers, thus facilitating the recycling of either or both of these materials.